Methoxy-functionalized covalent organic frameworks enable dipole-regulated charge separation and interfacial uranium recovery under ambient conditions.

Abstract

Photocatalytic uranium (U) recovery from water offers a sustainable route to couple radionuclide remediation with resource recycling, but covalent organic framework (COF) photocatalysts remain limited by inefficient visible-light utilization, rapid exciton recombination, poor wettability, and sluggish interfacial redox kinetics. Herein, we report a methoxy-functionalized triazine-based COF (TT-COF-OCH3) that integrates dipole regulation with hydrophilic pore engineering. Relative to the unsubstituted TT-COF-H and brominated TT-COF-Br analogues, methoxy substitution increases the molecular dipole moment, narrows the optical band gap, redistributes the frontier-orbital density, and promotes charge separation and transport. Under visible-light irradiation in air and without sacrificial agents, TT-COF-OCH3 achieves 99.82% U(VI) removal within 120 min and reaches a high uptake capacity of 1294 mg·g-1. It also maintains high removal efficiencies at pH 4-7 and in U(VI)-spiked water matrices containing representative competing ions, while retaining >85% removal efficiency after ten cycles. Spectroscopic and reactive-species analyses indicate that photogenerated electrons and superoxide-related intermediates participate in interfacial uranyl transformation, while in situ generated H2O2 induces the formation of insoluble uranyl peroxide hydrate. Uranium recovery therefore involves coupled adsorption, interfacial reduction, and peroxide mineralization. These findings show that substituent engineering can coordinate electronic polarization and interfacial wettability to accelerate charge separation, oxygen reduction, and uranium immobilization in COF photocatalysts.